1. Field of the Invention
The present invention relates to a method of producing a liquid ejection head that ejects a solution, in which charged particles are dispersed in a solvent, by means of an electrostatic force.
2. Description of the Related Art
Nowadays, a thermal-type ink jet head that ejects an ink droplet by means of an expansive force of a bubble generated in ink under heating and a piezo-type ink jet head that ejects an ink droplet by giving a pressure to ink using a piezoelectric element have been proposed. In the case of the thermal-type ink jet head, the ink is partially heated to 300° C. or higher, so that a problem arises in that a material for the ink is limited. Also, in the case of the piezo-type ink jet head, there is a problem in that its construction is complicated and an increase in cost is inevitable. As an ink jet head that solves those problems, a liquid ejection head is proposed which ejects a solution, in which charged particles are dispersed, by means of an electrostatic force (see JP 10-230607 A or JP 09-76505 A, for instance).
FIG. 17 is a schematic structural diagram of an example of an ink ejection means of an image recording apparatus disclosed in JP 10-230607 A. The ink ejection means 100 includes: a head substrate 102; an individual electrode 104 provided on the head substrate 102 so as to upwardly protrude, in which at least a surface of the individual electrode 104 has conductivity and a voltage is applied to the surface; an upper cover 106 having a construction where an upper cover through hole 106a is formed therein so as to correspond to the arrangement position of the individual electrode 104 and at least a tip end of the individual electrode 104 protrudes from the upper cover through hole 106a; and a counter electrode 110 provided in front of the tip end of the individual electrode 104, in which a recording medium 108 is arranged on a surface of the counter electrode 110. The individual electrode 104 has a notch formed as an ink guide groove 103 in a vertical direction in the drawing and functions as an ink guide that guides ink to a tip end side. The tip end of the individual electrode 104 is sharply pointed in a tapered shape having inclined surfaces and is set as a position at which an ink droplet is caused to fly.
The head substrate 102 and the upper cover 106 are arranged apart from each other by a predetermined distance and an ink 112, in which charged coloring material component particles (charged particles) are dispersed, is circulated in a gap between the head substrate 102 and the upper cover 106. The individual electrode 104 is set so that at least its tip end passes through the upper cover through hole 106a and protrudes toward a side of the counter electrode 110. A part of the ink 112 moves along the ink guide groove 103 by means of a capillary phenomenon and reaches the ink droplet ejection position. At the same time, the charged particles in the ink 112 also reach the ink droplet ejection position.
Here, if the charged particles are positively charged, voltages are applied to the individual electrode 104 and the counter electrode 110 so that the individual electrode 104 assumes a high potential and the counter electrode 110 takes a low potential. Also, if the charged particles are negatively charged, the voltage application is performed so that the individual electrode 104 assumes a low potential and the counter electrode 110 takes a high potential. As a result of the voltage application, an electric field is formed between the individual electrode 104 and the counter electrode 110 and charged particles existing at the ink droplet ejection position are attracted toward the counter electrode 110 side. As a result, an ink droplet containing the charged particles is ejected from the ink droplet ejection position toward the counter electrode 110. As disclosed in JP 10-230607 A, the ink ejected in this manner is caused to adhere onto the recording medium 108.
Here, in order to eject a smaller ink droplet with stability and efficiency, it is desired that the individual electrode 104 functioning as an ink guide member have a thinner and more pointed tip end. Also, in order to eject the liquid from multiple liquid ejection heads with stability, high density, and high precision, it is desired that an aspect ratio of the ink guide members (ratio of the height of the ink guide members to a cross section or breadth thereof) is increased and the ink guide members are provided on the head substrate with high density and high precision. Further, it is desired to uniformly form the sharp-pointed portions of the ink guide members. That is, it is desired to produce ink guide members, which each have a sharp-pointed portion and have a high aspect ratio, with high density and high precision as well as uniformly.
As a method of producing such ink guide members, JP 10-230607 A described above discloses a production method with which molding is performed using a plastic resin and multiple rows of ink guide members are arranged at predetermined pitches and intervals (see paragraphs [0016] and [0023] of JP 10-230607 A).
Also, as another method, JP 09-76505 A discloses a production method utilizing an Si semiconductor microprocessing technique. The outline of the ink guide member production method disclosed in JP 09-76505 A will be described below with reference to FIGS. 18A to 18G.
FIGS. 18A to 18G each shows a step of the ink guide member production method disclosed in JP 09-76505 A that utilizes the Si semiconductor microprocessing technique. First, as shown in FIG. 18A, a thermal oxidation layer 204 is formed on a surface of an Si single crystal substrate 202 and a resist layer 206 is formed on the thermal oxidation layer 204. Next, as shown in FIG. 18B, the resist layer 206 is patterned through exposure, development, and the like so as to have a mask pattern in a square shape or the like on the surface and the thermal oxidation layer 204 is etched using the resist layer 206 as a mask. Next, as shown in FIG. 18C, after the resist layer 206 is removed, the Si single crystal substrate is subjected to anisotropic etching and a concave portion 205 having an inverted-pyramid shape is formed. Next, as shown in FIG. 18D, the thermal oxidation layer 204 is removed once, and then another thermal oxidation layer 208 is formed on the entire surface. Next, a line-shaped convex portion 207 is formed on the inner surface of the concave portion 205 of the thermal oxidation layer 208 by vapor deposition using glass or the like. Next, as shown in FIG. 18E, an electric conductor is selectively sputtered using a selection mask (not shown) and an electrode layer 210 is formed so as to fill the inside of the concave portion 205. Then, as shown in FIG. 18F, a glass substrate 220 is bonded to the electrode layer 210 using an electrostatic bonding method or the like. Finally, as shown in FIG. 18G, the Si single crystal substrate 202 is etched and removed, thereby obtaining an ink guide member 200 that has a sharp-pointed tip end and ink guide grooves 214 that guide ink to the tip end on side surfaces.
With this production method, the concave portion is formed through patterning using photolithography at a time, so that it is possible to produce multiple ink guide members having high precision of position on the substrate. Also, the anisotropic etching of the Si single crystal substrate is utilized at the time of the formation of the concave portion, so that it is possible to form ink guide members having high precision, uniformity, and reproductivity.
With the above-mentioned production method disclosed in JP 10-230607 A with which a plastic resin is cast-molded using a separately produced mold and the solidified plastics are pulled out of the mold, however, if a molded structure has a high aspect ratio, there arises a problem in that the plastics cannot be pulled out of the mold and is broken, which makes it impossible to perform molding into a desired shape. Therefore, it is difficult to produce ink guide members having a high aspect ratio. Also, with this method, it is required to arrange the multiple molded ink guide members on the substrate while increasing precision of position. However, a degree, to which the precision of arrangement of the ink guide members can be increased, is limited. In addition, there is another problem in that a large number of process steps are required in order to arrange the ink guide members.
Also, with the production method disclosed in JP 09-76505 A that utilizes the Si semiconductor microprocessing technique as described above, the electrode layer 210 is formed with the sputtering method using the selection mask, so that it is required to form a film having a certain thickness. However, such a thick film tends to be distorted or warped due to a stress or the like. Therefore, it is difficult to form the film in a desired shape. Also, when a film having a certain thickness is to be selectively formed using the selection mask, it is required to space the mask apart from the substrate in accordance with the thickness of the film to be formed. Therefore, a degree of widening of the cross-sectional shape of the electrode layer 210 with respect to the opening of the selection mask increases as the thickness of the electrode layer 210 functioning as the ink guide member is increased, which makes it impossible to form an electrode layer having a high aspect ratio. Consequently, it is impossible to form an ink guide member having a high aspect ratio. Also, with this method, there is another problem in that the design flexibility of the shape of the electrode layer 210 is low, the process steps become complicated, and an increase in cost is inevitable.